Vinyl Pyridine Latex (V.P. Latex) is a versatile adhesive till date for the
treatment of various synthetic fabrics like rayon, nylon, polyester and aramid
fiber to improve their adhesion in fabric reinforced composite e.g. carcass in
tire, V-belt and conveyor belt etc. ¹ Vinyl Pyridine Latex is a heterogeneous
dispersion of ter-polymer of styrene, butadiene and vinyl pyridine in water. In
the practical utilization of lattices, either dilute or concentrated, the word
stability can be used in many different ways²´³, and stability may be required:

(a) To electrolyte addition
(b) To shear or mechanical work
(c) To freezing
(d) To heat or Sterilization
(e) To Long term Storage
(f) To drying conditions such that instantaneous re-dispersion is obtained on
rewetting.

In this present article category (E) will primarily be considered.

All hetero-phase systems are generally affected by different environmental
conditions. The various environmental conditions may alter the latex properties
as well as the polymer properties. As Vinyl Pyridine latex is also a
hetero-phase system hence therefore its final properties during storage may
change under environmental conditions. Around the globe storage conditions are
different ranging from subzero to as high as 50ºC temperature and hence it was
necessary to study the effect of various environmental conditions on VP Latex
during storage.

EXPERIMENTAL

(i) Preparation of Latex

The vinyl Pyridine-Styrene-butadiene terpolymer latex is produced by peroxy
disulphate-initiated emulsion co-polymerization by using a Rosin acid/Fatty acid
emulsifiers at 50-60ºC using reaction system similar to those for the production
of styrene butadiene lattices at this temperature. Rate of conversion is
monitored by measuring % nonvolatile matter (NVM) from the reactor samples at an
interval of two hours. After completion of reaction the latex is subjected to
degassing and then final modification is done and packed (I).

(ii) Packing Drums

The latex was packed in clean, virgin UMHDPE drums having 210 kg net latex
weight with dimension of 910 x 50mm. Drums were named as A, B and C according to
their environmental conditions as given below:

Drum No.

Storage Conditions

Duration (in months)

IdentificationMarks
graphs

A

B

C

Under direct sunlight

(Min 22.0ºC to

Max 50.0ºC)

Under Shade

(Min 22.0ºC to

Max 42.00ºC)

Under Storage

(Min 5.0ºC to

Max 1.00ºC)

February, ’01-July, ‘01

February, ’01-July, ‘01

February, ’01-July, ‘01

Series –1

Series –2

Series -3

*All the experiments as carried out at vadodara, India.

(iii) Sampling

Sample from each drums were taken (after rolling the drums for 30 minutes) once
in every month and subjected to analysis.

(a) Skin formation
As it is shown in Table-1, skin formation more in case of drum with is stored in
direct sunlight. But in other case there is no such observation. This skin
formation is attributed to the rapid evaporation of latex at higher temperature
as it is continuously exposed to the direct sunlight but in higher temperature
as it is continuously exposed to the direct sunlight but in other cases this is
not true and hence skin formation is not possible.

(b) %NVM

All the observations in different environmental conditions are reported in
Table-1 and plotted in Fig. 1. As it is seen in Fig. 1 the % NVM in case of drum
B and C is almost constant and whatever little variation is there which is
because of the experimental error- But on other hand in drum C it shows a slight
downward trend. This trend is observed because f the thick skin formation in the
drum where this like amount of solid goes out of phase

1. As few millimeter of empty space is left out during packing of the drums so
that much of space is occupied by air, Air contains CO2 Which gets converted to
mild acid e.g., H2CO3 in presence of moisture by Characteristic adsorption –
desorption phenomenon. This mild acid in turn reduce the pH of lattices during
storage.

2. During Processing few ingredients (such as initiator) is left out in ppm
level after completion of reaction. These ingredients get converted into very
mild acids in a long run which again contributes to the lower or pH in due
course of storage and which is prominent in elevated temperature.

(d) Brookfield Viscosity
Brookfield Viscosity is one of the important parameter of any liquid material.
This is directly related to particle size and % NVM of the Material. The change
is Viscosity is reported in Table –1 and plotted in Fig. 3. As it is seen in
Fig. 3 the BPV in case of drum B and C is slight varying and whatever little
Variation is there is because of the experimental error. But in other hand in
drum C it shows a slight downward trend. This trend is observed because of the
thick skin formation in the drum where little amount of solid goes out of phase.
Due to the low solid compared to other the drop in viscosity is clearly
observed.

(e) Surface Tension

Surface Tension is one of the important Parameter of any emulsion polymerized
latex. This a directly related to the emulsifier concentration in the latex. As
it is seen in Fig. 4, Surface tension is almost found constant in all the three
different case of drums A little bit of difference which is observed this is may
be due to the experimental error.

(f) Mechanical Stability
\
Mechanical Stability is very important in case of the latex as it is mainly used
in dipping of synthetic fabrics In dipping operation the latex is subjected to a
very high shearing force and mechanical stability testing is a simulation test
for the same. The variation in mechanical stability is shown in Fig, 5. As it is
seen from the figure that in all the cases there is a constant deterioration
with respect to storage time. But this is more prominent in case of drum, A
which was kept under direct sunlight. This is directly related to pH during
storage.

(g) Chemical Stability

Chemical Stability is another important factor for VP latex dipping. In dipping
operation the latex is subjected to different chemicals e.g., resorcinol and
formaldehyde etc. Chemical stability is done to verify the stability of the
lattices against those chemical stability is shown in Fig. 6. As it is seen from
the figure that in all the cases the trend is almost same with respect to
storage time.

(h) Particle Size

Particle size is he controlling factor of any lattices for all their intrinsic
properties. As it is shown in the graph (Fig. 7) there is no such variation in
the particle size of the latex during storage as it is directly related to
micelles which are not liable to change during this small storage time without
any external addition.

(i) Mooney Viscosity

Mooney Viscosity is polymeric property which is related to the molecular aspects
of dry polymer. It can be seen from the Fit. 8 that the polymer exits in the
heterogeneous dispersed phase which does not come in direct contact with the
environmental condition. This is further supported by the infrared spectroscopic
results as given in Fig. 9.

(j) IR Spectroscopy

Fig 9. (a) Shows the infrared spectrographs of vinyl pyridine-styrene butadiene
polymer in 15.15.70 ratio just after packing. The characteristics peak at 1470
cm-¹ is attributed to the presence of vinyl pyridine respectively in the main
chain polymer. Fig.9 (b.c and d) shows the IR curves after 6 months of latex
storage. As the graph shows there is no change in the characteristic curve of
the polymers which shows that no functional group develops in the main chain
during storage.

As it can be seen in the IR graphs that there is no change in the composition of
polymer when it is tested in initial stage and after six months of storage. This
confirms the money viscosity trend as shown in Fig. 8.

(k) Microbial Growth

Bacterial growth is very harmful to any emulsion system. Particularly it is very
prominent to VP latex as because the system contains fatty acid and rosin acid
which are very good food for bacteria. With the advent of bacterial growth the
emulsifiers may be consumed which in turn will remove the emulsifier layer in
the particles. The result will be coagulation of latex. In present system no
microbial growth was observed even after six months in all cases because the
system contains an effective bactericide.

CONCLUSION

From the above study it is very clear that exposure to direct sunlight
deteriorate the latex properties drastically. But the latex can be stored under
shade with a temperature varying from – 5 to 40ºC Without any drastic change in
various properties for six months.